...............controlled by two "three-way" wall switches,...................Three-way switches are called that because they have three connections, a common and two lines. From my childhood immersion in things electrical, I knew this configuration as a single-pole double-throw (SPDT) switch. Apparently in British electrical circles, it's known as a two-way switch.
For 2 location, 2- 3 way switch.3 and up use 2-3 way switch on both ends and nth 4-way switch in between for more location.Example 3 location3way - 4 way - 3 way4 location3 way - 4 way - 4 way - 3 waynth location3 way - nth 4 way - 3 way